FIELD OF INVENTION
The invention relates to the field of integrated optics chips or devices and more particularly to the field of multifunction integrated optics chips such as those having integrated optic circuits formed on Lithium Niobate (LiNbO.sub.3) substrates. Integrated optics chips are designed to include waveguides and to perform functions such as "Y", "Y-Y", or Star spliters or couplers, WDM (Wavelength Dependent Couplers) and modulators. Multiple functions are incorporated on a single device eliminating losses and errors associated with individual interface optical coupling.
The devices are usually fabricated in large numbers on three to four inch wafers of Lithium Niobate (LiNbO.sub.3) using conventional photomasks, vacuum deposition, chemical baths and etching techniques to form large numbers of identical components at low cost and with high reliability. MIOC's (Multifunction Integrated Optical Chips or Components) or circuits capable of performing many of the aforementioned functions are necessary for the fabrication of middle and high accuracy fiber optic gyros (FOGS) or rotation sensors that rely on the principle of Sagnac interferometers and possibly other interferometric fiber optic sensors such as hydrophones that rely on the principles of the Mach-Zehnder or Michaelson Interferometers requiring high stability.
While investigating the reason for a transient effect that resulted in signal saturation which was observed while performing temperature cycle tests on FOGs, the inventors observed an electrical discharge or arc at the base of a de-lidded, packaged MIOC. The test MIOC chip was made of Lithium Niobate (LiNbO.sub.3) and was similar in size to the related art device shown in FIG. 1. The inventors related the discharge to a pyroelectric effect and calculated that a device of that width would generate voltages across the 2 mm width of the chip of above 100 volts per degree centigrade.
It was recognized that the pyroelectric effect observed might also be related to a FOG power hysteresis problem also under investigation in which a charge differential developed across the face of a MIOC chip due to temperature change. The hysteresis problem exhibits itself as a slight change in the transmitted power of a FOG instrument as the instrument is first taken through a positive or negative temperature change followed by a negative or positive temperature change. The charge differential that develops across the face of the chip results in a charge leakage across the face of the chip. The time and temperature dependent effects combine to contribute to a slight hysteresis in the transmitted power of the instrument and to the efficiency of the waveguides in the MIOC to propagate light.
As an initial solution, conductive paint or conductive epoxy was applied to the sides of test chips. The adhesive material used was a poor conductor. However, the test demonstrated that instruments which had previously failed due to saturation or hysteresis effects were able to pass an acceptance test when modified. A solution consisting of metallization on the + and -Z surfaces (the sides) of the chip and the use of conductive feet to electrically connect the +Z and -Z surfaces was proposed as a solution for the saturation or arcing effect. The word "feet" will be understood to be the plural of--foot--as used herein.
As further background, Integrated optics chips, such as those characterized in this application are formed using processes and steps similar to some of those found in related U.S. Patents such as U.S. Pat. No. 5,193,136 filed Nov. 26, 1991 for a "PROCESS FOR MAKING MULTIFUNCTION INTEGRATED OPTICS CHIPS HAVING HIGH ELECTRO-OPTIC COEFFICIENTS" which issued to Dr. Chin L. Chang et al on Mar. 9, 1993; U.S. Pat. No. 5,046,808 filed Dec. 18, 1989 for an "INTEGRATED OPTICS CHIP AND METHOD OF CONNECTING OPTICAL FIBER THERETO" which issued to Dr. Chin L. Chang On Sep. 10, 1991; U.S. Pat. No. 5,393,371 filed Jun. 21, 1993 for a "INTEGRATED OPTICS CHIPS AND LASER ABLATION METHODS FOR ATTACHMENT OF OPTICAL FIBERS THERETO FOR LiNbO.sub.3 SUBSTRATES" which issued to Dr. Chin L. Chang et al on Feb. 28, 1995; U.S. Pat. No. 5,442,719 for an invention titled "ELECTRO-OPTIC WAVEGUIDES AND PHASE MODULATORS AND METHODS FOR MAKING THEM" which issued to Dr. Chin L. Chang et al on Aug. 15, 1995; and U.S. Pat. No. 4,976,506, filed Feb. 13, 1989 for "METHODS FOR RUGGED ATTACHMENT OF FIBERS TO INTEGRATED OPTICS CHIPS AND PRODUCT THERE OF" which issued to Dr. G. Pavlath on Dec. 11, 1990. This application is being filed contemporaneously with a U.S. patent application Ser. No. 09/124,457, filed Jul. 28, 1998 based on docket number GCD 98-22; for a "Dual Purpose Input Electrode Structure For MIOCs (Multi-Function Integrated Optics Chips)" by Lorrie L. Gampp, Gregory A. Zimmerman, Christine E. Geosling and John P. Rahn.
Each of the foregoing patents have a common assignee, Litton Systems Inc. of Woodland Hills, Calif. Each of the foregoing patents cited herein are incorporated herein by reference for the purpose of providing those skilled in the art with background information on how integrated optics chips or multifunction integrated optics circuits are made.
In addition to the above patents, an early paper titled "Short-and Long-term Stability In Proton Exchanged Lithium Niobate Waveguides" by Janet Lehr Jackel and Catherine E. Rice of AT&T Bell Laboratories, Holmdel, N.J., 07733 appeared in SPIE Vol 460, Processing of Guided Wave Optoelectronic Materials (1984) at page 43.
This application is particularly directed to methods and apparatus for the reduction of errors produced in an integrated optics chip, formed to function as an optical modulator. The errors are produced by temperature changes which cause voltage differences across the surface of chip due to the Pyroelectric Effect.
The field that produces the voltage differences across the surface of the chip is caused by any change in the bulk temperature of the chip. A temperature gradient across the chip is not required to produce a voltage difference due to the pyroelectric effect. The effect is produced when ever the temperature of the chip is changed from one value to another such as from room temperature to 100 degrees fahrenheit.